1. Field of the Invention
This invention relates generally to a machine and method for blow molding a one-piece carbonated beverage bottle with an internal web structure positioned between two hand-grip depressions. Although not exclusively, a bottle blow molder will use a polyethylene terephthalate (PET) polyester material to make the bottle, a material having a molecular structure capable of biaxial orientation.
2. Description of the Prior Art
Carbonated beverage products are commonly contained in polyester bottles. This bottle typically comprises: a neck portion defining an opening, a shoulder portion depending therefrom, a closed base portion, and a sidewall portion extending between the base and shoulder portions. The sidewall portion typically has a cross-sectional shape circular in character.
The method for making polyester bottles by biaxially orienting its material structure is well known. The method requires a preform made first, usually with an injection molding process. This preform typically comprises: a neck portion defining an opening, a body portion depending therefrom, and an integral bottom portion depending from the body portion. The body portion defines a hollow space, with a circular cross-sectional shape, closed at the bottom portion and open at the neck portion.
The preform body and bottom portions are heated to a specific temperature and placed in a closed bottle blow molding cavity where a flow of high pressure air inflates the preform to form the bottle with a relatively uniform wall thickness. The specific temperature desired with polyethylene terephthalate material is about 105 degrees Celsius to about 120 degrees Celsius. The flow of high-pressure air (about 3800 kilopascals), often in combination with a mechanical means, stretches the preform and orients the molecular structure of the material in an axial direction. In addition, high-pressure air stretches the preform and orients the molecular structure of the material in a circumferential direction generally perpendicular to the axial direction. Commonly identified as biaxial orientation, this bi-directional molecular orientation of the polyester material generally enhances bottle strength and performance.
A well-known method to establish the specific temperature of the preform body and bottom portions is to place the preform onto a rotatable spindle within an oven. As the spindle moves along a path through the oven, the preform is rotated a specified distance from a controllable energy source for a specified time. Typically, shields prevent the neck portion of the preform from heating significantly. Machinery operators occasionally use reflectors or shields within the oven to direct heat away from or toward selected areas of the preform. When the preform achieves proper temperature, a mechanism positions it in the blow mold cavity. A second mechanism then inflates the preform to form the bottle.
The polyester material used to blow mold the bottle is a relatively poor conductor of heat energy. Injection molded polyethylene terephthalate material is unique in that it can assume an amorphous form, which is clear and transparent when unpigmented, or a semicrystalline form, which is usually opaque. When amorphous polyethylene terephthalate as found in the injection molded preform is heated for a sufficient time to a temperature between about 85 degrees Celsius and about 250 degrees Celsius large spherulitic crystals form causing the material to become opaque. The highest growth rate of crystals occurs at about 175 degrees Celsius, and at this temperature, the material, depending on its molecular weight and other factors, will become opaque in about 90 seconds. At 100 degrees Celsius the growth rate is several minutes.
The oven is at a significantly higher temperature than the desired temperature of the preform. During heat-treatment, the preform exterior overheats risking growth of spherulitic crystals, but the preform is inflated and subsequently cooled in the blow mold cavity before noticeable crystals actually form.
Because of its relatively large cross-sectional size, bottles containing approximately one liter of the carbonated beverage product or more are often difficult for a consumer to grip, particularly while pouring the beverage into a cup or glass.
U.S. Pat. No. 5,398,828, incorporated by reference, discloses a bottle for carbonated beverages intending to be easier to grip. The bottle has two generally opposed depressions in its sidewall to form a handgrip. An internal web structure between the two grip depressions prevents eversion of the hand-grip.
For making the bottle with the internal web structure supporting the hand-grip feature, U.S. Pat. No. 5,398,828 also discloses a preform, as described above, including an internal web portion extending completely across the hollow space from the bottom portion to the body portion and terminating in the body portion. When blow molded, the molecular structure of the material within the body, bottom, and web portions of the preform must now be biaxially oriented.
The method for heating or conditioning the preform to a specific temperature described above will treat a webbed preform sufficiently to allow the molding of a bottle.
However, inadequate heating of the web portion in the preform and inadequate cooling of the web portion in the blow molded bottle create crystalline structures, stresses, and web distortions that tend to degrade bottle performance and appearance. The web does not have a smooth flat appearance. Furthermore, the internal pressure created inside the bottle from the carbonated beverage act on structural stresses often causing the web portion to separate from the bottle sidewall portion. Adequately heating the preform web portion and cooling the bottle web portion requires additional care.
The object of this invention is to provide a method to heat the body portion, bottom portion, and web portion of the preform to specific temperatures without overheating any of those portions and to blow mold this preform into a bottle with reduced structural stresses and distortions and with a smooth and generally flat internal web structure.
The invention is a machine and a method for blow molding a bottle with an internal web structure between two hand-grip depressions from a preform. The preform features a neck portion with an open end, a body portion depending from the neck portion, a bottom portion depending from the body portion and forming a closed end. The neck portion, body portion, and bottom portion define a hollow space with a common axis and a circular cross-sectional shape. An internal web portion extends completely across the hollow space from the bottom portion and terminating within the body portion.
The machine basically features a means for in-feeding the preform; a means for heating the body portion, bottom portion, and internal web portion; a means for inflating the preform in a bottle blow mold cavity defining the hand-grip depressions; and a means for cooling the internal web structure of the bottle before removal from the bottle blow mold cavity.
The method basically includes the steps of in-feeding the preform; heating the body portion, bottom portion, and internal web portion of the preform; inflating the preform in a bottle blow mold cavity defining the hand-grip depressions; cooling the internal web structure of the bottle; and removing the bottle. from the bottle blow mold cavity.